This invention relates to shock absorbers for land vehicles, especially tracked military vehicles such as tanks and personnel carriers. Certain features of the invention could be applied to wheeled vehicles used off the highways, e.g. military trucks. A principal aim of the invention is to provide a hyraulic shock absorber wherein the metered flow out of the shock absorber chamber can be varied or regulated in accordance with different types of terrain and different vehicle speeds.
In conception of the invention it was realized that vehicle shock absorbers should exhibit higher damping at low terrain irregularity input frequencies and lower damping at high terrain irregularity input frequencies. In general greater dampener action is desired when the vehicle is traversing terrain having widely spaced terrain irregularities; less dampener action is desired when the vehicle is traversing terrain having closely spaced terrain irregularities.
FIG. 7 is a graph plotting some factors that influence or determine desired damping action on oscillatory road wheel motion. In the graph:
.zeta. is a damping ratio factor. A low value of .zeta. corresponds to low damping; a high value of .zeta. indicates high damping, PA1 .omega..sub.n is the natural oscillation frequency of the system, PA1 .omega. is the impressed oscillation frequency due to terrain irregularities, and PA1 T.R. is the transmissibility ratio (applicable to force or displacement).
Vehicle ride action is improved by achievement of a low transmissibility ratio, i.e., a decrease in the transmitted force to the sprung mass and human occupants. At relatively low impressed oscillation frequencies .omega. a low transmissibility ratio is achieved by using heavy damping, i.e., .zeta. factor near 1; at relatively high impressed oscillation frequencies (where .omega./.omega..sub.n is above .nu.2) a low transmissibility ratio is achieved by using light damping or no damping, i.e., a .zeta. factor near 0. A desirable system is one in which the damping action is inversely varied according to variations in the impressed oscillation frequency, i.e., the frequency of terrain irregularities. In most systems damping is in effect only during jounce (upward) motion of the road wheel. Rebound (downward) motion of the road wheel is undamped.
In general, when the terrain irregularities are close together the road wheel should be capable of relatively fast jounce (upward) motion to keep in step with terrain irregularities; low dampener effect is desired. When the terrain irregularities are more widely spaced a greater dampener effect is required to maintain desired suspension forces and hull position.
In judging or estimating terrain irregularity frequencies it is necessary to consider the effect of vehicle speed. High vehicle speeds effectively cause a given set of terrain irregularities to be relatively close together, while low vehicle speeds effectively cause the same terrain irregularities to be relatively far apart, i.e., a fast-moving vehicle sees a given pattern of terrain irregularities to be closer together than would a slow-moving vehicle.
My invention also takes into account the fact that when a vehicle is required to traverse a high-amplitude terrain irregularity, such as a log or rock, the shock absorber should preferably exert a relatively slight dampener effect during jounce motion, i.e., the road wheel should be capable of relatively fast motion in the jounce direction.
My invention is directed to a vehicle shock absorber wherein the jounce motion dampener action can be varied inversely according to the frequency of terrain irregularities, i.e., a high dampener effect at low terrain irregularity frequencies and a low dampener effect at higher terrain irregularity frequencies. The shock absorber system is preferably designed to anticipate high amplitude terrain irregularities, such as rocks or logs, whereby minimum dampener effect is exerted on the jounce motion while the vehicle is traversing the high amplitude irregularity.
When the invention is applied to a military tank or similar gun-carrying vehicle the shock-absorber system may include control features to increase damping in the suspension system while the gun is being fired, i.e., during recoil and counterrecoil. A highly damped system is believed to contribute to a relatively stable gun platform during on-the-move firing.
In carrying out the invention I incorporate in the individual shock absorbers power-operated metering valves. Electric signals of regulated strength are applied to the valve power operators to reposition the metering valves for either a high flow rate, a low flow rate, or an intermediate flow rate. The metered flow rate determines the rate of fluid flow through the hydraulic shock absorption chamber, and hence the dampener action.
The improved shock absorbers may be manually controlled by the human driver in accordance with the ride action being experienced. Alternately the shock absorbers may be controlled by a computer having electrical inputs reflective of the terrain in the path of the vehicle and/or accelerometer measurement of hull dislocation.